Clamping device, in particular for thin-walled hollow parts

ABSTRACT

The invention concerns a clamping device comprising a tensioning spindle whereof one end has a first axially fixed support surface and whereof the other end has a second axially mobile support surface and mobile relative to the first support surface through a clamping element. Between the two support surfaces on the tensioning spindle are one or several elastomer adapter sleeves.

BACKGROUND

During the machining of hollow thin-walled parts, for example sleeves,which are machined only on their outer side but not on their inner side,there is the problem that the unmachined inner side used for clampingthe part has shape errors, for example non-roundness, generally inconjunction with non-uniform wall thickness in the circumferentialdirection or deviations from the straight cylindrical shape, undercertain circumstances likewise in conjunction with wall thicknessdifferences in the longitudinal direction. If a conventional clampingdevice is used, the parts are deformed elastically when being clampedin, on account of these shape errors of their inner side. As a result,during the machining of the parts, the shape errors of the inner sideare, so to speak, transferred to the outer side. Therefore, it is notpossible to achieve either high shape accuracy or a very high surfacequality, and in addition cylindricity can barely be maintained.Therefore, the lower the wall thickness and the greater the length ofthe parts, the less consideration is given to clamping such thin-walledparts at their two end faces since they then deviate more or lessseverely under the cutting forces. In addition, the parts then tend tooscillate, so that chatter marks are additionally produced.

SUMMARY OF THE INVENTION

The invention is based on the object of providing a clamping device withwhich, primarily, very thin-walled and relatively long parts can beclamped satisfactorily, largely independent of irregularities of theirinner surface, and their outer side can be machined with the requiredaccuracy and surface quality. According to a preferred embodiment of thepresent invention, a clamping device may have the following features:there is a clamping spindle (11) which, at least at one end, is providedwith coupling elements (12) for coupling to the main spindle of amachine tool, the clamping spindle (11) has a first supporting face (17)at one end which is aligned axially and faces the other end of theclamping spindle (11) and which is arranged on the clamping spindle (11)such that it cannot be displaced in the axial direction; there is asecond supporting face (21) on the clamping spindle (11) at the otherend, which is aligned axially and faces the one end and which isarranged on a clamping element (19) which is guided on the clampingspindle (11) such that it can be displaced in the axial direction; thereis a clamping device (15), by means of which the clamping element (19)with the second supporting face (21) can be displaced relative to thefirst supporting face (17) and can be fixed while applying an axialclamping force to the clamping spindle (11); there is at least oneclamping sleeve (13), which is produced from an elastomer, whose innerdiameter is matched to the outer diameter of the clamping spindle, whoseend faces are matched to the first supporting face (17) and to thesecond supporting face (21); a clamping sleeve (13) has a plurality ofsupporting strips (23) on its outer side, which are produced from ametallic material, which are permanently connected to the clampingsleeve (13), which are arranged distributed uniformly on thecircumference of the clamping sleeve (13) and whose outer side (29)forms a cylinder surface section in each case which is matched to theinner diameter of the part (24).

Similar problems also occur during the machining of the inner side ofthin-walled parts whose outer side remains unmachined, in particularwhen the parts are relatively long. The invention is therefore alsobased on the object of providing a clamping device with which,primarily, very thin-walled and relatively long parts can be clampedsatisfactorily, largely independent of irregularities of their outersurface, and their inner side can be machined with the required accuracyand surface quality. In a preferred aspect of the present invention, theclamping device (15) is formed by a longitudinal section (18) of theclamping spindle (11) that is provided with an external thread and by aclamping ring (19) matched thereto and having an internal thread.

The fact that, instead of rigid clamping jaws, a clamping sleeve made ofan elastomer is used and is guided on a smooth cylindrical clampingspindle and is compressed axially via its two end faces means that thequasi hydraulic behavior of the material of the clamping sleeve isutilized in order to compensate to a large extent for irregularities inthe clamping surface of the part. The fact that there are metallicsupporting strips on the outer side of the clamping sleeve means thatabrasion of the clamping sleeve is avoided when the parts are pushed onand pulled off and, as a result, a higher lifetime of the clampingdevice and, at the same time, constant clamping security and clampingaccuracy are achieved.

The clamping device may be adapted more easily to different lengths ofthe parts. In a preferred aspect, there are a plurality of clampingsleeves (13), which are axially displaceably guided on the clampingspindle (11) and which are arranged between the first supporting face(17) on the clamping spindle (11) and the second supporting face (21) onthe annular clamping element (19).

In another aspect, the axial frictional force which occurs when theclamping sleeves are being clamped, between the clamping sleeve and itsseating surface on the clamping spindle or on the basic body, isdistributed over a plurality of relatively short sections where saidforce is lower, individually and overall. As a result, the radialclamping force of the clamping device is also distributed, at leastapproximately uniformly, over the entire clamping length. The fact thatthe clamping sleeve is designed to be shorter than its supporting sleeveand does not project beyond the end faces of the supporting sleeve, andthat the transmission of the axial clamping force is performed byinterposed pressure rings prevents the compliant clamping sleeves beingpressed into the initially open interspaces between the supportingsleeves and damaged in the process at the start of the clampingoperation. In a preferred aspect, for each clamping sleeve (13) there isa supporting sleeve (14), which is produced from a material whosedimensional stability is greater than the dimensional stability of theclamping sleeve (13), whose inner diameter is matched to the outerdiameter of the clamping spindle (11) and to whose outer diameter theinner diameter of the clamping sleeve (13) is matched; the supportingsleeves (14) may have a greater length than the clamping sleeves (13);each clamping sleeve (13) may be arranged on its supporting sleeve (14)in such a way that each of the end faces of the clamping sleeve (13)does not project in the axial direction beyond the end faces of thesupporting sleeve (14); a pressure ring (25) may in each case bearranged between two successive clamping sleeves (13), whose innerdiameter is matched to the outer diameter of the supporting sleeves (14)and whose outer diameter is at most equal to the inner diameter of thepart (24).

In another aspect, when the clamping device is operated, the clampingsleeves can be compressed only by the differential amount of the lengthdimensions. This results in an exactly defined radial clamping forceand, in addition, as a result overstressing both of the elastic clampingsleeves and of the thin-walled parts is avoided. In a preferred aspect,the sum of the axial extent of the pressure ring (25) and of theclamping sleeve (13) is greater by a predefined amount (26) than theaxial extent of the supporting sleeve (14) of the latter.

In another aspect, the number of components of the clamping device isreduced. In a preferred aspect, each pressure ring (25) is detachably ornon-detachably connected to the end of a supporting sleeve (14),preferably produced in one piece with it.

In another aspect, the radial diameter change of the clamping sleeve isdisproportionate to the axial compression movement. The same applies toa configuration according to claim 8 and according to claim 18,respectively, a greater transmission factor between the radial diameterchange and the axial compression movement being achieved. In a preferredaspect, on the clamping spindle, the seating face for each clampingsleeve is formed as the outer surface of a truncated cone, which widenstoward the first supporting face, and the inner face of the clampingsleeve is matched to its seating face. In another preferred aspect, onthe supporting sleeve (27), the seating face (28) for the clampingsleeve (31) is formed as the outer surface of a truncated cone, and theinner face (32) of the clamping sleeve (31) is matched to its seatingface (28) on the supporting sleeve (27).

In another aspect, the clamping spindle or the base body can besupported at its second end, so that it gives way elastically to alesser extent under the cutting forces and, as a result, the machiningaccuracy remains constant over the entire length of the part. In apreferred aspect, at its end facing away from the coupling elements(12), the clamping spindle (11) has an outer and/or an inneraccommodation face (55; 56) for a supporting device (57).

In another aspect, a clamping device which can be produced and operatedrelatively simply is provided. In a preferred aspect, the clampingdevice (15) is formed by a longitudinal section (18) of the clampingspindle (11) that is provided with an external thread and by a clampingring (19) matched thereto and having an internal thread.

BRIEF DESCRIPTION OF THE DRAWINGS

In the following text, the invention will be explained by using a numberof exemplary embodiments illustrated in the drawings, in which:

FIG. 1 shows a partly sectioned view of a first embodiment of a clampingdevice having a plurality of clamping sleeves for the external clampingof parts;

FIG. 2 shows an end view of a clamping sleeve;

FIG. 3 shows a plan view of a clamping sleeve;

FIG. 4 shows an enlarged detail from FIG. 1 with two clamping sleeves;

FIG. 5 shows an enlarged detail similar to FIG. 4 with two modifiedclamping sleeves;

FIG. 6 shows an enlarged detail similar to FIG. 4 with two furthermodified clamping sleeves;

FIG. 7 shows a longitudinal section of a further embodiment of theclamping sleeves;

FIG. 8 shows a longitudinal section, shown as a detail, of a seconddesign of the clamping device having a plurality of clamping sleeves forthe external clamping of parts.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS

The clamping device 10 that can be seen from FIG. 1 has, as mainsubassemblies or main components, a clamping spindle 11 having couplingelements 12, a plurality of clamping sleeves 13 each having a supportingsleeve 14 and a clamping device 15. In the upper half, the clampingdevice 10 is illustrated in the clamped state and, in the lower half, inthe unclamped state.

The clamping spindle 11 is an elongate, circularly cylindrical bodywhich, at its end on the left in FIG. 1, is detachably or non-detachablyconnected to the coupling elements 12, by means of which it can becoupled to the main spindle of a machine tool. At its left-hand end, theclamping spindle 11 is provided with a collar 16, whose planar, annularend face facing away from the coupling elements 12 serves as a firstaxial supporting face 17 of the clamping sleeves 13. Arranged at theother end of the clamping spindle 11 is the clamping device 15. It isformed by a longitudinal section 18 provided with an external thread anda clamping ring 19 matched thereto and provided with an internal thread.The planar, annular end face of the clamping ring 19, facing the firstsupporting face 17, forms a second supporting face 21 for the clampingrings 13. For reasons of simpler manufacture and for improved possibleadaptation to different adjustment stipulations, it may be expedient toinsert a pressure ring 22 between the second supporting face 21 of theclamping ring 18 and the nearest clamping sleeve 13.

As can be seen from FIG. 2 . . . FIG. 4, the clamping sleeves have theshape of a straight annular cylinder. They are produced from anelastomer. Arranged on their outer side are a plurality of supportingstrips 23 of a metallic material. These supporting strips 23 arepermanently connected to the clamping sleeve 13. They are alignedparallel to the axis and arranged distributed uniformly on thecircumference of the clamping sleeve 13. The outer side of thesupporting strips 23 forms a cylinder surface section which is matchedto the inner diameter of the part 24 which, in FIG. 1 and to some extentin the other figures, is indicated dash-dotted.

The clamping sleeves 13 can be pushed directly onto the shaft of theclamping spindle 11. The inner diameter of the clamping sleeves 13 isthen matched to the outer diameter of the clamping spindle 11. However,it is more expedient to push each clamping sleeve 13 onto a supportingsleeve 14. The supporting sleeves 14 are produced from a material whosedimensional stability is greater than the dimensional stability of thematerial of the clamping sleeve 13. Good sliding pairing between thematerial of the clamping sleeves 13 and that of the supporting sleeves14 is advantageous. A metallic material is also considered for thispurpose. The inner diameter of the supporting sleeves 14 is matched tothe outer diameter of the clamping spindle 11. The outer diameter of thesupporting sleeves 14 is matched to the inner diameter 13 of theclamping sleeves 13 or vice-versa. The supporting sleeves 14 have agreater length than the clamping sleeves 13. Each clamping sleeve 13 isarranged on its supporting sleeve 14 in such a way that each of the endfaces of the clamping sleeve 13 does not project in the axial directionbeyond the end face of the supporting sleeve 11.

FIGS. 4 and 5 reveal two different embodiments of the supporting sleeve14, which for the purpose of distinction are designated supportingsleeve 14.1 (FIG. 4) and supporting sleeve 14.2 (FIG. 5), respectively.

In the respective lower half of the illustrations, the clamping sleeves13 are shown in the unclamped state and, in the upper half, in theclamped state. In the unclamped state (lower half), the outer side ofthe clamping sleeve 13 and, in particular, that of its supporting strips23 has a smaller spacing from the inner face of the part 24 which, forclarity, is illustrated greater than is actually the case. In theclamped state (upper half), the outer side of the clamping sleeves 13and that of their supporting strips 23 rest on the inner side of thepart 24. The radial clamping movement of the clamping sleeves 13 neededfor this purpose is effected by means of axial compression of theclamping sleeves 13. Conversely, the radial unclamping of the clampingsleeves 13 is effected by means of axial relieving of the load on theclamping sleeves 14. Both are effected by the clamping device 15. Inthis arrangement, the clamping sleeves 13 are clamped in between thefirst supporting face 17 on the clamping spindle 11 and the secondsupporting face 21 on the clamping ring 18 (FIG. 1).

If the clamping sleeves 13 are not seated directly on the clampingspindle but each on a clamping sleeve 14, the clamping sleeves 13 areshorter than their supporting sleeves 14. The axial compression force ofthe clamping device 15 is then transmitted from one clamping sleeve 13to the next by means of a pressure ring 25 in each case. In theembodiment according to FIG. 5, these pressure rings 25 are independentparts, as pressure rings 25.2, whose inner diameter is matched to theouter diameter of the associated supporting sleeves 14.2. Their outerdiameter is at most equal to the inner diameter of the part 24. In theembodiment according to FIG. 4, the pressure rings 25.1 are permanentlyconnected to the associated supporting sleeves 14.1, to be specificexpediently produced in one piece with them.

Both in the embodiment according to FIG. 4 and in the embodimentaccording to FIG. 5, the clamping sleeves 13, their supporting sleeves14 and the pressure rings 25 are expediently configured in such a waythat, in the unclamped state of the clamping sleeves 13, the sum of theaxial extent of the pressure ring 25 and of the clamping sleeve 13 isgreater, by a predefined axial distance 26 (FIG. 4), than the axialextent of their supporting sleeve 24.

As a result, in the clamped state of the clamping sleeves 13, thesupporting sleeves 14 form a stop which prevents the clamping sleeves 13being compressed axially by the clamping device 15 beyond an extentmatched to the relevant part 24 and, as a result, being widenedradially.

FIGS. 6 and 7 reveal two modified embodiments of clamping sleeves andtheir supporting sleeves.

On the supporting sleeve 27, the seating face 28 for the clamping sleeve31 is formed as the outer surface of a truncated cone. The inner face 32of the clamping sleeve 31 is matched to the seating face 28, that is tosay it is formed as a hollow outer surface of a truncated cone.

In the embodiment according to FIG. 7, on the supporting sleeve 33 theseating face 34 for the clamping sleeve 35 is formed by a plurality oflongitudinal sections 34.1 . . . 34.5 of the outer surface of atruncated cone. The inner face 36 of the clamping sleeve 35 is formed bylongitudinal sections, matched thereto, of the outer surface of a hollowtruncated cone. The seating-face sections 34.1 . . . 34.5 follow oneanother axially in the same alignment. They adjoin one another via anannular planar interface 37 in each case.

In the embodiment according to FIG. 7, the cone angle of the seatingfaces 34 and the inner face 36 is considerably greater than in theembodiment according to FIG. 6. As a result, during a predefined axialcompression travel, the radial expansion of the clamping sleeve 35 isgreater than in the clamping sleeve 31.

FIG. 8 reveals a clamping device 40 for the external clamping ofthin-walled sleeve-like parts 41, which are machined on their innerside. The coupling elements for coupling to a machine tool are notillustrated.

The clamping device 40 has a hollow base body 42 having theapproximately hollow cylindrical inner space 43. At one end of the innerspace 43, on the base body 42, there is a first supporting face 44 whichis aligned axially and faces the other end.

Arranged in the inner space 43 of the base body 42 are a plurality ofclamping sleeves 45, which are produced from an elastomer. The innerface 46 of the clamping sleeves 45 forms the clamping face for the part41. It is provided with a number of supporting strips, as is the case inthe clamping face on the outside of the clamping sleeves 13 of theclamping device 10. The clamping sleeves 45 are each seated in asupporting sleeve 47, which is produced in one piece together with apressure ring 48 in each case. The axial compression required for theradial clamping movement of the clamping sleeves 45 is effected by aclamping device 51, which is formed by a longitudinal section providedwith an internal thread on the inner face of the basic body 42 and by anannular clamping ring 53 screwed into the latter.

In the case of the clamping device 40, the operative direction of itsparts in the radial direction is opposite to that in the correspondingparts of the clamping device 10 (FIG. 1). Taking account of this fact,their parts largely correspond to one another in terms of constructionand operating mode. To this extent, reference is made to the descriptionof this clamping device 10, which also includes the modificationsaccording to FIG. 5 . . . FIG. 7.

As is indicated on the right in FIG. 1, in particular in the case ofparts of greater length and/or lower diameter and smaller wallthickness, and in the case of an appropriately designed clamping device,it may be expedient to clamp the clamping device not only at the endhaving the coupling elements for the connection to the main spindle of amachine tool but also to support it at the opposite end. This can bedone in different ways, for example via a supporting face located on theoutside and/or via one located on the inside.

Outside the clamping device 15, the clamping spindle 11 has both theouter cylindrical supporting face 55 and, in its end face, the centeringhole 56 as an inner supporting face. A co-rotating lathe center 57 actstogether with said centering hole 56. For the outer supporting face 55,a freely co-rotating or a driven chuck can be used.

What is claimed is:
 1. A clamping device for clamping a part,comprising: a clamping spindle; and at least one clamping sleeve,wherein said clamping spindle comprises: coupling elements for couplingsaid clamping spindle to a main spindle of a machine tool; a firstsupporting face at one end which is aligned axially and faces the otherend of the clamping spindle and which is arranged on the clampingspindle such that it cannot be axially displaced; a clamping elementaxially displaceably arranged on the clamping spindle at the other end;and a second supporting face which is aligned axially and faces the oneend and which is arranged on the clamping element, wherein said at leastone clamping sleeve is produced from an elastomer, wherein said at leastone clamping sleeve has end faces that are matched to the firstsupporting face and to the second supporting face, wherein said at leastone clamping sleeve has a plurality of supporting strips on its outerside, wherein said plurality of supporting strips are produced from ametallic material, are permanently connected to the clamping sleeve, arearranged distributed uniformly on a circumference of the clampingsleeve, and whose outer side forms a cylinder surface section which ismatched to an inner diameter of the part.
 2. The clamping device asclaimed in claim 1, further comprising a plurality of clamping sleeveswhich are axially displaceably guided on the clamping spindle and whichare arranged between the first supporting face on the clamping spindleand the second supporting face on the clamping element.
 3. The clampingdevice as claimed in claim 2, wherein for each clamping sleeve there isa supporting sleeve which is produced from a material whose dimensionalstability is greater than the dimensional stability of the clampingsleeve, whose inner diameter is matched to an outer diameter of theclamping spindle, whose outer diameter is matched to an inner diameterof the clamping sleeve, and whose length is greater than the clampingsleeves, wherein each clamping sleeve is arranged on its supportingsleeve in such a way that each of the end faces of the clamping sleevedoes not axially project beyond end faces of the supporting sleeve,wherein the clamping device further comprises a pressure ring in eachcase arranged between two adjacent clamping sleeves, wherein saidpressure ring has an inner diameter that is matched to the outerdiameter of the supporting sleeves and an outer diameter that is at mostequal to the inner diameter of the part.
 4. The clamping device asclaimed in claim 3, wherein a sum of an axial length of the pressurering and of the clamping sleeve is greater by a predefined amount thanan axial length of the supporting sleeve of the latter.
 5. The clampingdevice as claimed in claim 3, wherein each pressure ring is connected toan end of a supporting sleeve.
 6. The clamping device as claimed inclaim 1, further comprising, on the clamping spindle, a seating face foreach clamping sleeve that is formed as the outer surface of a truncatedcone, which widens toward the first supporting face, wherein an innerface of the clamping sleeve is matched to its seating face.
 7. Theclamping device as claimed in claim 3, further comprising, on thesupporting sleeve, a seating face for each clamping sleeve that isformed as the outer surface of a truncated cone, wherein an inner faceof the clamping sleeve is matched to its seating face on the supportingsleeve.
 8. The clamping device as claimed in claim 3, furthercomprising, on the supporting sleeve, a seating face for the clampingsleeve that is formed by a plurality of longitudinal sections of theouter surface of a truncated cone which follow one another axially inthe same alignment and which adjoin one another via an interface in eachcase.
 9. The clamping device as claimed in claim 1, wherein, at its endfacing away from the coupling elements, the clamping spindle has anaccommodation face configured to accommodate a supporting device. 10.The clamping device as claimed in claim 1, wherein the clamping spindleis provided with an external thread and the clamping element comprises aclamping ring having an internal thread matched to the external thread.11. A clamping device for clamping a part, comprising: an at leastpartly hollow base body; and at least one clamping sleeve, wherein saidbase body comprises: coupling elements for coupling said base body to amain spindle of a machine tool; a first supporting face at one end of aninner space of the base body which is aligned axially and faces theother end of the base body and which is arranged on the base body (42)so as to be nondisplaceable axially; a clamping element axiallydisplaceably arranged on the base body at the other end; a secondsupporting face at the other end of the inner space of the base bodywhich is aligned axially and faces the one end and which is arranged onthe clamping element, wherein said at least one clamping sleeve isproduced from an elastomer, wherein said at least one clamping sleevehas end faces that are matched to the first supporting face and to thesecond supporting face on the base body, wherein said at least oneclamping sleeve has a plurality of supporting strips on its inner side,wherein said plurality of supporting strips are produced from a metallicmaterial, are permanently connected to the clamping sleeve, are arrangeddistributed uniformly on a circumference of the clamping sleeve, andwhose inner side forms a cylinder surface section which is matched to anouter diameter of the part.
 12. The clamping device as claimed in claim11, further comprising a plurality of clamping sleeves which are axiallydisplaceably guided in the inner space of the base body and which arearranged between the first supporting face on the base body and thesecond supporting face on the clamping element.
 13. The clamping deviceas claimed in claim 12, wherein for each clamping sleeve there is asupporting sleeve which is produced from a material whose dimensionalstability is greater than the dimensional stability of the clampingsleeve, whose outer diameter is matched to an inner diameter of theinner space of the base body, whose inner diameter is matched to anouter diameter of the clamping sleeve, and whose length is, greater thanthe clamping sleeves, wherein each of the clamping sleeves is arrangedon its supporting sleeve in such a way that each of the end faces of theclamping sleeve does not axially project beyond the end face of itssupporting sleeve, wherein the clamping device further comprises apressure ring in each case arranged between each two adjacent clampingsleeves, wherein said pressure ring has an outer diameter that ismatched to the inner diameter of the supporting sleeves and an innerdiameter that is at least equal to the outer diameter of the part. 14.The clamping device as claimed in claim 13, wherein a sum of an axiallength of the pressure ring and the clamping sleeve is greater by apredefined amount than an axial length of the supporting sleeve.
 15. Theclamping device as claimed in claim 13, wherein each pressure ring isconnected to an end of a supporting sleeve.
 16. The clamping device asclaimed in claim 11, further comprising on the base body, a seating facefor each clamping sleeve that is formed as the outer surface of a hollowcone, which tapers toward the first supporting face, wherein an outerface of the clamping sleeve is matched to its seating face on the basebody.
 17. The clamping device as claimed in claim 13, furthercomprising, on the supporting sleeve, a seating face for each clampingsleeve that is formed as the outer surface of a hollow cone, wherein anouter face of the clamping sleeve is matched to its seating face on thesupporting sleeve.
 18. The clamping device as claimed in claim 13,further comprising, on the supporting sleeve, a seating face for theclamping sleeve that is formed by a plurality of longitudinal sectionsof the outer surface of a hollow cone which follow one another axiallyin the same alignment and which adjoin one another via an interface ineach case.
 19. The clamping device as claimed in claim 11, wherein, atits end facing away from the coupling elements, the base body has anouter accommodation face configured to accommodate a supporting device.20. The clamping device as claimed in claim 11, wherein the base body isprovided with an internal thread and the clamping element comprises aclamping ring having an external thread matched to the internal thread.21. The clamping device as claimed in claim 1, wherein said at least oneclamping sleeve has an inner diameter that is matched to an outerdiameter of the clamping spindle.
 22. The clamping device as claimed inclaim 5, wherein said pressure ring is produced in one piece with saidsupporting sleeve.
 23. The clamping device as claimed in claim 11,wherein said at least one clamping sleeve has an outer diameter that ismatched to an inner diameter of the base body.
 24. The clamping deviceas claimed in claim 15, wherein said pressure ring is produced in onepiece with said supporting sleeve.